Patent GB-626613-A (GB)
Title: Improvements in direct current motors for obtaining a rapid rise in speed thereof
IPC: H02P7/34
Filed: 1945-07-10
Abstract: 626,613. Control of D.C. motors. MOZZANINI, G. G., and LEBERTRE, M. July 10, 1945, No. 17564. Convention date, May 1, 1942. [Class 38 (iii)] In a system arranged to accelerate a motor rapidly from rest, as in a planing machine, rolling mill, &c., a resistance is inserted in series with the pre-adjusted field rheostat for a brief starting period, and a resistance which is connected in parallel with the rheostat during normal running is disconnected, to provide a reduced energization of the field winding until the motor attains the speed required, whereupon the first mentioned resistance is short-circuited and the other connected in parallel with the rheostat. In this manner the motor is accelerated from rest on a characteristic curve corresponding to a speed greater than that required, and as soon as the required speed is attained the initial characteristic is abandoned. The system is applicable also to the generator field of a Ward Leonard system, in which case the field is increased during starting, and subsequently decreased. In the field control of a motor a resistance 2, Fig. 3, is in series with the field coil 12 and rheostat 3, and the connection of a fixed resistance 5 and the short circuiting of the whole or a tapped portion of resistance 2 is controlled by the contacts 1a, 1b of a relay 1. The coil of relay 1 is connected in a control circuit associated with a differential relay comprising a coil 6 which is connected in a constant voltage circuit provided with a rheostat 8 which can be pre-set in accordance with the speed required from the motor. The other coil 6<SP>1</SP> of the differential relay may be connected in series with a relay coil 9 of a safety device, and is energized by a tachometer generator 7 driven by the motor being controlled. Closure of a control switch in the circuit of coil 6 effects also the closure of a delayedopening switch 10, so that relay contacts 6a are closed and relay 1 is energized from a feeder circuit or connection. This causes the relay contacts 1a, 1b to open and the motor is started with rheostat 3 and resistance 2 in series with the motor field 12. As the motor speeds up, the coil 9 is energized to close contacts 9a before the timeswitch 10 opens, so that relay 1 is maintained energized until the motor reaches a speed such that the current in tachometer fed coil 6' counteracts coil 6, whereupon contacts 6a open and relay 1 is deenergized to allow the contacts to resume the position shown in Fig. 3, whereby the motor field current is increased. In the event of a break or bad contact in the circuit of coil 6', control is taken from coil 6 by the de-energization of coil 9- and opening of contacts 9a. The rheostat 8 controlling the coil 6, and the motor field rheostat 3, may be regulated by a common member 14. When applied to the generator field of a Ward Leonard system the sequence of operations is the reverse of that for motor field control, the contacts 1a, 1b, Fig. 3, being closed until the generator voltage attains a predetermined value. The system in its respective forms may be applied to the motor field and generator field of a Ward Leonard system. Specification 625,565 is referred to.